This invention relates in general to fluid seals. More specifically, this invention relates to gaskets that connect two sealing portions, which prevent fluid leakage between the two, while reducing the contact pressure between the two members.
In general, conventional gaskets require a relatively high compressive load between the members being sealed in order for the gasket to provide an effective seal over time. For example, a conventional gasket placed between two stationary members, such as an engine block and an oil pan, or a cylinder head and a valve/cam cover, is compressed between these elements under a relatively high contact pressure in order to produce an effective seal. A significant reason that a very high contact pressure is required is because these conventional gaskets lose their sealing force over time. A conventional rubber gasket, for example, may lose as much as ninety-percent of its initial loading over time, so the initial sealing force needs to start out very high to account for this degradation.
Moreover, in the applications that require the high compressive sealing load, the number and placement of fasteners must compensate for deflections caused by the high loading conditions in order to assure a good seal all of the way around the gasket. Often, then, the number of fasteners will be increased just to account for the high initial compressive sealing load.
Additionally, these highly compressed gaskets can become a medium for transmitting vibrations, thus creating poor noise, vibration and harshness (NVH) isolation characteristics between the two members. That is, the vibration load input from one member is easily transferred through the gasket to the other member.
Examples of such conventional gaskets requiring a high sealing load between the members include an elastomeric gasket, shaped as an O-ring or similar shape, as well as an edge bond gasket, a carrier gasket, and a rubber coated metal (RCM) gasket. All of these conventional gaskets require a high compressive sealing load to assure an effective seal between the members, so the effectiveness of vibrational isolation of one member from the other is poor and the number of fasteners needed for sealing may be higher than is necessary for securing the two members together. Another example of a conventional gasket is one formed from a room temperature vulcanite (RTV) located between the two members. The RTV is applied as a liquid in a thin layer and cures when exposed to air. For effective sealing with the RTV, however, it requires a hard mount between the members, which also provides poor vibration isolation.
In many applications, including automotive applications, it is desirable to reduce the transmission of vibrations. A reduction of the transmission of vibrations can result in a reduction in noise and harshness, so it is desirable to reduce the transmission of vibrations between two sealed elements, such as an engine block and an oil pan—or engine head and rocker/cam cover. Also, in order to minimize the cost of and time to assemble two members together, it is desirable to minimize the number of fasteners required for effective sealing.
Thus, it is desirable to have a gasket that will properly seal between two members while minimizing the compressive sealing force required.